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United States Patent | 5,778,029 |
Kaufmann | July 7, 1998 |
A signal conditioner comprising several embodiments of transversal (FIR) filters that utilize symbol addressed multiplier lookup tables. In particular, five embodiments in accordance with the principles of the present invention are described. The present invention generates a predistorted waveform within the transversal filter that provides for compensation for the effects of nonlinear amplifiers and intersymbol interference. The present invention may be employed to digitally generate an arbitrary baseband waveform that represents a limited alphabet of symbols. The present invention dramatically simplifies the implementation of FIR filters where the application of the FIR filter is to provide a transversal filter function for waveforms that represent symbols. The degree of simplification is related to the number of bits that define the size of the symbol alphabet as compared to the number of bits required to adequately represent a digital sample of the waveform. Typically 2, 3 or 4 bits represent the alphabet of communication symbols, whereas waveforms require as a minimum 8 bits of quantization. A second aspect of the present invention comprises combining the function of generating arbitrary waveforms with the symbol addressed lookup tables that are part of the FIR filter. The waveform is precompensated to minimize the effect of intersymbol interference and is prewarped to compensate for transmitter nonlinearities.
Inventors: | Kaufmann; John (Palo Alto, CA) |
Assignee: | Lockheed Martin Aerospace Corporation (Bethesda, MD) |
Appl. No.: | 634514 |
Filed: | April 18, 1996 |
Current U.S. Class: | 375/296; 332/103; 375/298 |
Intern'l Class: | H04L 025/03; H04L 027/36 |
Field of Search: | 375/229,230,232,235,266,284,285,297,278,296,295,198 333/18,28 R,138,139,165,166,167,202,203 364/724.01,724.03,724.14,724.16,724.19,724.2,572 332/107,123,124,159,160,103,104 327/261 330/10,149 455/126,127,91 |
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4291277 | Sep., 1981 | Davis et al. | 330/149. |
4430743 | Feb., 1984 | Watanabe | 375/15. |
4800572 | Jan., 1989 | Nossek et al. | 375/232. |
4805189 | Feb., 1989 | Mahoney | 375/11. |
4975927 | Dec., 1990 | Yoshida | 375/15. |
5025234 | Jun., 1991 | De Luca | 375/235. |
5200977 | Apr., 1993 | Ohnishi et al. | 375/235. |
5200978 | Apr., 1993 | Lo Curto et al. | 375/15. |